Reserve battery cells are characterized, as the name implies, by the ability to maintain anode and cathode portions of the cell in a dry or unactivated state prior to use. To achieve activation, the electrolyte necessary for battery operation is fed to the individual cells whereupon an electric current may emanate from the cell terminals through an external load.
FIG. 1 depicts a typical prior art approach to the activation of a reserve battery containing a number of cells. Turning to FIG. 1, a stack 10 of individual cells 21, each containing its own anode and cathode, is provided in a dry or unactivated state. As such, the cells are capable of being used years after initial manufacture with little or no loss of potential energy.
When activation is desired, an activation signal is provided by closing switch 22 which sparks electrical match 23 and ignites propellant 24. The force of expansion of the propellant generates gas sufficient to rupture or burst diaphragms 25, 26 and 27 and put pressure upon the electrolyte located in reservoir 28. Being a liquid, the electrolyte is relatively incompressible and thus the force generated by the gas generator propellant causes diaphragms 29 and 30 to rupture, allowing the electrolyte to pass within manifold entry 31 and into individual cells 21.
As cells 21 fill, there is generally an overflow of electrolyte which passes through vent tube 32 into sump 33. Relief valve 34 is provided for the venting of trapped gas downstream of the passing electrolyte.
Although the structure depicted in FIG. 1 is more than adequate to activate a reserve cell, certain inherent difficulties are experienced by this typical prior art approach to the activation problem. The most common problem observed is that after activation, a pool of electrolyte is caused to appear in each cell and throughout the manifold which provides a current leakage path between cells. In other words, there is simply no liquid seal which is formed after the activation process is carried out. In addition, the interconnecting electrolyte paths can result in parasitic capacity losses after activation but before use of the battery as well as an unwanted gas pressure buildup and, in extreme cases, catastrophic battery short-circuiting via metal deposition within the manifold housing. The only requisite for current leakage is a continuous path of conductive electrolyte between cells. This provides the necessary potential difference to support electrochemical reactions which result in metal deposition and electrolysis within the affected battery assembly. Substantial elimination of this apparent problem is fully disclosed in applicant's co-pending U.S. application Ser. No. 762,332 filed on Aug. 5, 1985.
Yet another disadvantage inherent in the use of prior art designs is the inability to prevent fluids other than the electrolyte from entering the cell housing and contacting the anode and cathode collector. Quite frequently, gases which are generated in the expansion of the propellant speedily tunnel their way through the electrolyte and enter the battery housing prior to a complete filling of the housing by the electrolyte itself. This diminishes electrolyte-anode/cathode current collector contact and thus reduces the performance characteristics of the cell.
It is thus an object of the present invention to provide a reserve battery cell which can be activated at will without experiencing any of the disadvantages inherent in the known prior art designs.
It is yet a further object of the present invention to provide a reserve battery cell which is capable of being activated and which inherently insures that electrolyte and only electrolyte passes within the cell housing.